Apparatus For Manufacturing Ultrafine Fiber And Method For Manufacturing Ultrafine Fiber

ABSTRACT

The apparatus for producing ultrafine fibers includes a nozzle portion, a laser irradiation unit, and a drawing chamber. The nozzle portion has an inlet for feeding a raw fiber, a first jet outlet which communicates with the inlet and jets a first drawing gas stream for delivering and drawing the raw fiber, and a second jet outlet which is arranged in the periphery of the first jet outlet and jets a second drawing gas stream. The laser irradiation unit on which the nozzle portion is installed irradiates a laser light to the raw fiber delivered from first jet outlet to melt the raw fiber. The drawing chamber draws the melted raw fiber by using the first drawing gas stream and the second drawing gas stream which are jetted from the nozzle portion.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a national stage entry under 35 USC § 371 of International Application No. PCT/JP2018/024577, filed on Jun. 28, 2018, which claims priority to Japanese Patent Application No. 2017-126325 filed on Jun. 28, 2017, the disclosures of which are herein incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an apparatus and to a method for producing ultrafine fibers. The present invention more particularly applies to nanofiber spinning by a laser drawing method in which raw fibers are melted by laser light and the fibers are drawn by a drawing gas stream that is jetted from a nozzle.

BACKGROUND ART

Patent Document 1 discloses a method for producing nanofibers by laser drawing. Patent Document 2 proposes a method for producing nanofibers using vibration spinning of a multifilament. The method in Patent Document 2 improves poor productivity and uniformity which are problems in the technique of Patent Document 1. In Patent Document 2, the multifilament is fed into a nozzle and vibrated so that, from the viewpoint of forming a plurality of nanofibers, the nanofibers can be produced with high productivity. Additionally, since a large number of nanofibers is generated from one orifice and are blown at random by vibration, a highly uniform nonwoven fabric can be obtained with a reduced number of orifices.

REFERENCE DOCUMENT LIST Patent Documents

-   Patent Document 1: WO2008/084797 -   Patent Document 2: WO2015/141495

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

It is important in the technique of Patent Document 2 to control a vibration angle of the multifilament, and if the vibration angle is significantly large, melted raw yarns and drawn fibers may come into contact with a nozzle surface. When the melted raw yarns come into contact with an orifice surface, and when the drawn fibers fly around a drawing gas stream and the drawn fibers and the like adhere to the surroundings of the nozzle to contaminate the nozzle, a stable operation for a long time may not be possible. Additionally, when the vibrational state of the multifilament is unstable, melted lumps (resin masses called “shot beads”) of the raw yarn resin may be generated. The melted lumps may adhere to a product and deteriorate its quality.

The present invention has been made in view of the circumstances described above. An object of the present invention is to provide an apparatus for producing ultrafine fibers and a method therefor capable of producing the ultrafine fibers stably for an extended time and reducing the amount of resin mass generated due to poor drawing.

Another object of the present invention is to provide a producing apparatus and a producing method by which ultrafine fibers can be produced stably for an extended time with higher productivity and the quality of a product can be improved by preventing the drawn ultrafine fibers from adhering to the nozzle portion.

Means for Solving the Problem

According to one aspect of the present invention, there is provided an apparatus for producing ultrafine fibers which includes a nozzle portion having an inlet for feeding a raw fiber, a first jet outlet which communicates with the inlet and which jets a first drawing gas stream for delivering and drawing the raw fiber, and a second jet outlet which is arranged in a periphery of the first jet outlet and which jets a second drawing gas stream; a laser irradiation unit which is installed on the nozzle portion to irradiate laser light to the raw fiber delivered from first jet outlet and melt the raw fiber; and a drawing chamber for drawing the melted raw fiber by using the first drawing gas stream and the second drawing gas stream which are jetted from the nozzle portion.

Additionally, in the apparatus for producing ultrafine fibers, the second drawing gas stream has a slower flow speed than the first drawing gas stream.

Furthermore, the first and the second drawing gas streams are generated by a pressure difference between inside and outside of the drawing chamber.

Furthermore, the apparatus for producing ultrafine fibers of the present invention further includes a speed adjustment mechanism for controlling a flow speed of the second drawing gas stream.

The speed adjustment mechanism includes a valve or a regulator.

Furthermore, the apparatus for producing ultrafine fibers of the present invention further includes a speed controller for adjusting an amount of air flowing to the second jet outlet, wherein the speed controller is operated to control the flow speed of the second drawing gas stream.

The apparatus for producing ultrafine fibers of the present invention further includes a sensor for detecting the flow speed or a flow rate of the second drawing gas stream, a speed controller for adjusting an amount of air flowing to the second jet outlet, and a control device for controlling the speed controller based on the flow speed or the flow rate of the second drawing gas stream detected by the sensor and controlling the flow speed of the second drawing gas stream.

Furthermore, the second jet outlet is provided concentrically on the periphery of the circular first jet outlet, and the second drawing gas stream is generated to surround a periphery of the first drawing gas stream.

Furthermore, the second jet outlet is holes of a porous metal member installed in the periphery of the first jet outlet.

Furthermore, the nozzle portion includes a plurality of the inlets and the first jet outlets, and the second jet outlets are provided in the peripheries of the first jet outlets, respectively.

Still further, according to another aspect of the present invention, there is provided a method for producing ultrafine fibers, which includes feeding a raw fiber to an inlet of a nozzle portion and delivering the raw fibers from a first jet outlet which communicates with the inlet to a drawing chamber; irradiating the raw fiber delivered to the drawing chamber with laser light to melt the raw fiber; and drawing the melted raw fiber by using a first drawing gas stream for drawing the raw fiber which is jetted from the first jet outlet and a second drawing gas stream which is jetted from a second jet outlet arranged in a periphery of the first jet outlet.

Effects of the Invention

According to the above-configured apparatus and method for producing ultrafine fibers, the melted fibers are drawn by means of the first drawing gas stream and the second drawing gas stream in the periphery of the first drawing gas stream, so that droplets which cause contamination and are generated when the fibers are drawn by the first drawing gas stream are blown by the second drawing gas stream and can be suppressed from adhering to the periphery of the first jet outlet of the nozzle. Moreover, the second drawing gas stream is generated in the periphery of the first drawing gas stream, so that the vibration range of the fibers protruding from the first jet outlet where the first jet outlet serves as the starting point is restricted, and shaking of the fibers is suppressed. Thus, the amount of resin mass generated can be reduced. Therefore, it is possible to provide the apparatus for producing ultrafine fibers and a method thereof capable of producing the ultrafine fibers stably for a long time and reducing the amount of resin mass generated due to poor drawing.

Additionally, the droplets which cause contaminants can be suppressed from adhering to the periphery of the first jet outlet of the nozzle, and thus, less cleaning of the nozzle portion and the extended continuous operation time of the producing apparatus are possible. Furthermore, since the amount of resin mass generated can be reduced, the resin mass adhered to the product can be reduced, and the quality of the product can be improved. As a result, it is possible to provide the producing apparatus and the producing method that can produce ultrafine fibers stably for a long time with higher productivity, and can improve the quality of the product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically illustrating an apparatus for producing ultrafine fibers according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a first configuration example of a nozzle for producing ultrafine fibers which is used in the producing apparatus of FIG. 1.

FIG. 3A is an enlarged cross-sectional view of a tip portion of the nozzle as illustrated in FIG. 2.

FIG. 3B is an enlarged plan view of the tip portion of the nozzle as illustrated in FIG. 2.

FIG. 4 is a cross-sectional view illustrating a second configuration example of the nozzle for producing ultrafine fibers which is used in the producing apparatus of FIG. 1.

FIG. 5 is a cross-sectional view illustrating a third configuration example of the nozzle for producing ultrafine fibers which is used in the producing apparatus of FIG. 1.

FIG. 6 is a perspective view schematically illustrating an apparatus for producing ultrafine fibers according to a second embodiment of the present invention.

FIG. 7 is a perspective view schematically illustrating an apparatus for producing ultrafine fibers according to a third embodiment of the present invention.

FIG. 8 is a cross-sectional view illustrating a configuration example of the nozzle for producing ultrafine fibers which is used in the producing apparatus of FIG. 7.

FIG. 9A illustrates the adhesion state of contaminants to a tip portion of a conventional nozzle for producing ultrafine fibers.

FIG. 9B illustrates the adhesion state of contaminants to a tip portion of the producing nozzle according to the first configuration example of the present invention.

FIG. 9C illustrates the adhesion state of contaminants to the tip portion of the producing nozzle according to the first configuration example of the present invention when the producing conditions are changed.

FIG. 10A is an enlarged view illustrating the adhesion state of contaminants in FIG. 9A.

FIG. 10B is an enlarged view illustrating the adhesion state of contaminants in FIG. 9C.

FIG. 11A illustrates the adhesion state of resin mass to a nanofiber sheet which is produced by a conventional producing apparatus.

FIG. 11B illustrates the adhesion state of resin mass to a nanofiber sheet which is produced by the producing apparatus of the present invention.

FIG. 12A illustrates the adhesion state of contaminants to a tip portion of another conventional nozzle for producing ultrafine fibers.

FIG. 12B illustrates the adhesion state of contaminants to a tip portion of a nozzle for producing ultrafine fibers of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

First Embodiment

The present invention relates to a method and an apparatus for producing ultrafine fibers having a fiber diameter (diameter) of 10 nm to 1 μm, preferably 30 nm to 800 nm.

FIG. 1 illustrates the apparatus for producing the ultrafine fibers according to the first embodiment of the present invention, and is a schematic configuration diagram of the so-called carbon dioxide gas laser supersonic drawing device. This apparatus produces ultrafine fibers (nanofibers) 40 in a drawing chamber 21. The drawing chamber 21 is installed on a movable base 22 that can move in the x, y, and z directions, and the movable base 22 is mounted on a fixed base 23. A raw fiber (monofilament or multifilament) 25 wound around a fiber feed reel 24 is guided from the inlet of the nozzle 10 which serves as the fiber feed orifice to the jet outlet. The high polymer material (thermoplastic polymer material) which is melted by heat is applicable as the raw fiber 25, and various materials such as polyester, biodegradable polymer, hardly soluble polymer, and super engineering plastic can be applied.

More specifically, the raw fiber 25 is made of a thermoplastic resin capable of being processed into a yarn. Examples of such thermoplastic resin include: polyester resins such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, polyglycolic acid, and polyarylate, polyamide resins such as nylons (nylon 6, nylon 12, and nylon 66) and aromatic polyamides, polyolefin resins such as polypropylene and polyethylene, polyvinyl alcohol polymers such as ethylene-vinyl alcohol copolymers and ethylene-vinyl acetate copolymers, polyacrylonitrile polymers, fluorinated polymers such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFAs), ethylene-tetrafluoroethylene copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, and polyvinylidene fluoride, polyurethane polymers, polyvinyl chloride polymers such as polyvinyl chloride and polyvinylidene chloride, polystyrene polymers such as polystyrene and syndiotactic polystyrene, poly(meth)acrylic polymers such as polymethacrylate methyl, polyoxymethylene, ether-ester polymers, cellulose polymers such as cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate, polyurethane resins, polyacetal resins, polycarbonate resins, modified polyphenylene ether resins, polyphenylene sulfide resins, polysulfone resins, polyethersulfone resins, polyetherketone resins, polyimide resins, polyetherimide resins, and engineering plastics such as liquid crystal polymers (LCPs). Examples of the thermoplastic resins for the raw filaments may further include any combination of the above polymers and/or may optionally contain one or more additives such as a plasticizer, a surfactant and an antioxidant. Among the above, polyethylene terephthalate, polylactic acid, nylons (nylon 6 and nylon 66), and polypropylene are especially suitable for use in production of ultrafine fibers due to their good drawing and molecular orientation properties. Examples of the thermoplastic resins for the raw filaments may further include any combination of the above polymers and/or may optionally contain one or more additives such as a plasticizer, a surfactant and an antioxidant. Among the above, polyethylene terephthalate, polylactic acid, nylons (nylon 6 and nylon 66), and polypropylene are especially suitable for use in production of ultrafine fibers due to their good drawing and molecular orientation properties.

Additionally, when the raw fiber 25 is multifilament, the multifilament of a bundle of at least 10 monofilaments (filaments) is used. The number of monofilaments to be bundled is appropriately adjusted depending on the ratio of the size of the jet outlet of the nozzle 10 to be used and the total cross-sectional area of the multifilament. For example, the multifilament constituted by at least 10 monofilaments, preferably at least 20 monofilaments, and more preferably, at least 40 monofilaments, is used. The diameters of filaments constituting the multifilament range from 10 to 200 μm. The multifilament is twisted so that a plurality of filaments does not lose integrity as a bundle or does not fall apart. The number of twists is, for example, at least 20 times/m) but is appropriately adjusted depending on the number, shape, material, or the like, of multifilaments.

A laser irradiation unit 26 on which the nozzle 10 is installed is installed on top of the drawing chamber 21. When the drawing chamber 21 is depressurized by the vacuum pump (not illustrated), the air flows from the nozzle 10 into the drawing chamber 21 due to the pressure difference between the inside and the outside of the drawing chamber 21 to generate a first drawing gas stream 16. A second drawing gas stream 17 having a slower flow speed than the first drawing gas stream 16 is generated in the periphery of the first drawing gas stream 16.

In this state, the laser is irradiated from the carbon dioxide gas laser oscillator 27 through the irradiation window 28 to the raw fiber 25 protruding from the jet outlet of the nozzle 10 to partially dissolve the raw fiber 25, and the melted fiber is drawn by the first drawing gas stream 16 and the second drawing gas stream 17 to produce nanofibers (ultrafine fibers) 40.

At this time, if the flow speed of the second drawing gas stream 17 is too fast, the vibration of raw yarn may be destabilized, and if the flow speed is too slow, the effect is weakened. Thus, it is preferable that the pressure in the drawing chamber 21 be adjusted, and the flow rate be adjusted by installing a valve in the passage that generates the second drawing gas stream 17.

Additionally, the fiber diameter of the nanofibers 40 can be controlled relatively easily by changing the drawing conditions such as the feeding speed of the raw fiber 25, the output of the carbon dioxide gas laser oscillator 27, and the pressure difference between the inlet side and the jet outlet side of the nozzle 10.

In FIG. 1, the laser irradiation unit 26 is provided with a laser transmission window 29 at the position facing the irradiation window 28. A power meter 30 for measuring the output of the carbon dioxide gas laser is arranged on the transmission window 29.

First Configuration Example of the Nozzle

FIG. 2 illustrates the first configuration example of the nozzle for producing the ultrafine fibers which is used in the producing apparatus of FIG. 1. The nozzle 10 has the double structure that an inner nozzle portion 12 is accommodated in an internal space 11 a in an outer nozzle portion 11 having a cylindrical outer shape. The inner nozzle portion 12 has a hollow cylindrical shape in which the side of the first inlet 14 of the raw fiber is widened and the side of the first jet outlet 15 that communicates with the first inlet 14 is narrowed. A first passage 13 through which the raw fiber and the air (indicated by arrow A1) pass is formed along the central axis XA inside the inner nozzle portion 12. The first drawing gas stream 16 which draws the melted fiber is generated from the first jet outlet 15 due to the pressure difference between the first inlet 14 side and the first jet outlet 15 side.

A second passage 18 that generates the second drawing gas stream 17 having a slower flow speed than the first drawing gas stream 16 is formed in the boundary region between the outer nozzle portion 11 and the inner nozzle portion 12. A second jet outlet 19 is provided concentrically on the periphery of the circular first jet outlet 15 of the inner nozzle portion 12, and the second jet outlet 19 jets the second drawing gas stream 17 that flows through the second passage 18. In this example, an extended portion 18 a in which a part of the second passage 18 is expanded is formed. The extended portion 18 a works as the chamber that suppresses the change of flow speed of the second drawing gas stream 17 that is generated by the air (indicated by an arrow A2) drawn from the second inlet 20.

The factors that determine the flow speed of the first drawing gas stream 16 of the inner nozzle are the pressure difference between the side of the first inlet 14 and second inlet 20 and the side of the first jet outlet 15 and second jet outlet 19, and the area ratio of the first inlet 14 to the first jet outlet 15. On the other hand, the factors that determine the flow rate of the second drawing gas stream of the outer nozzle are the pressure difference between the side of the first inlet 14 and second inlet 20 and the side of the first jet outlet 15 and second jet outlet 19, and the area ratio of the portion with the smallest cross-sectional area in the second passage 18 to the second jet outlet 19. Furthermore, the speed ratio of the first drawing gas stream 16 to the second drawing gas stream 17 is important when securing the stability of spinning and obtaining the contaminants inhibition effect of the double nozzle. According to the experiment, the desired range of the flow speed ratio of the first drawing gas stream 16 to the second drawing gas stream 17 (second drawing gas stream 17/first drawing gas stream 16) is 1.0 to 0.1.

For example, as illustrated in the enlarged views in FIGS. 3A and 3B, the tip portion of the nozzle 10 preferably has the diameter Φa of the first jet outlet 15 in the range of 0.1 mm to 3.0 mm, and the appropriate diameter is chosen depending on the thickness and fineness of the yarn to be used. Additionally, the inner diameter Φb of the second jet outlet 19 ranges from 0.1 mm to 0.5 mm, and the value as close as possible to Φa (that is, the thinner wall thickness) is desirable for generating the good gas stream. On the other hand, a certain degree of wall thickness is required owing to restrictions on mechanical strength and metal processing accuracy. The outer diameter Φc ranges from 2.0 mm to 10 mm. While satisfying these conditions, the conditions expressed by Φc>Φb, Φc<inter-nozzle distance (in the case of multiple nozzles) and the like also need to be met. By taking them into consideration, the inner diameter Φb is set as 0.2 mm and the outer diameter Φc is set as 4 mm, for example.

Furthermore, the first jet outlet 15 is located in the inside of the second jet outlet 19 by T which ranges from 0 mm to 1.0 mm, for example, by 0.2 mm, so that the first jet outlet 15 can be suppressed from being damaged during the cleaning of the tip portion of the nozzle 10. If T is 0 to 0.5 mm, the level of adverse effect on spinning is negligible. When offset over 1.0 mm is applied, the larger the amount of offset becomes, the more unstable the vibration spinning state is. Note that La ranges from 0.1 mm to 10 mm, and Lc ranges from 0.1 mm to Φc. If La/Φa becomes too large, yarn clogging is likely to occur. Lc is of a length that does not occlude the second passage 18. By taking them into consideration, a preferable example is expressed by, La=3×Φa, and Lc=0.9×Φc.

In this case, the pressure P1 in the drawing chamber 21 and the pressure P2 in the raw fiber feeding chamber are expressed by P1>P2, preferably P1≥2P2, more preferably P1≥3P2, and most preferably P1≥5P2. The pressure difference between P1 and P2 (P1−P2) is specifically preferably 20 kPa or more, more preferably 50 kPa or more, and most preferably 70 kPa or more. By having such a pressure ratio, the first drawing gas stream 16 becomes a subsonic to supersonic speed region.

The raw fiber fed from the first inlet 14 of the nozzle 10 is guided to the first jet outlet 15, and while the second drawing gas stream 17 is jetted from the second jet outlet 19 to the surroundings of the first drawing gas stream 16, the laser is irradiated to the raw fiber protruding from the first jet outlet 15 to partially dissolve the raw fiber, and the melted fiber is drawn by the first drawing gas stream 16 and the second drawing gas stream 17 to produce the ultrafine fibers.

Although the raw fiber fed from the first inlet 14 can be monofilament, using the multifilament raw yarn generates a large number of nanofibers from one nozzle 10 so that the productivity can be improved. The “multifilament” is a bundle of monofilaments. No particular limitation is imposed on the cross-sectional shape of the monofilaments constituting the multifilament, and various modified cross-section raw yarns such as circular, ellipsoidal, tetragonal, trigonal, trapezoidal, or polygonal cross-sections may be used. Hollow yarns and composite raw yarns such as sheath-core raw yarns and side-by-side raw yarns may also be used. Furthermore, the raw yarns constituting the multifilament may be different from each other. The multifilament may consist of monofilaments having different cross-sectional shapes and/or different materials.

By using the nozzle 10 having the above-described configuration, while the second drawing gas stream 17 is generated from the second jet outlet 19 to the surroundings of the first drawing gas stream 16, the laser is irradiated to partially dissolve the raw fiber 25. Consequently, the droplets which cause contaminants and are generated when the fiber is drawn by the first drawing gas stream 16 are blown downward by the second drawing gas stream 17, and the droplets can be suppressed from adhering to the surroundings of the first jet outlet 15 of the nozzle 10. Furthermore, the second drawing gas stream 17 is generated from the second jet outlet 19 to the surroundings of the first drawing gas stream 16, so that the vibration range of the fibers (vibrators) protruding downward from the first jet outlet 15 where the first jet outlet 15 serves as the starting point is restricted, and shaking of the fibers can be suppressed. Thus, the amount of resin mass generated due to poor drawing can be reduced.

The above-described producing apparatus and method require less cleaning of the nozzle 10, and thus, the continuous operation time of the producing apparatus can be extended. Additionally, the resin mass is suppressed from adhering to the product (for example, nanofibers 40 or nanofiber nonwoven fabric) so that the quality can be improved. Therefore, the spinning technology can be further developed.

Second Configuration Example of the Nozzle

FIG. 4 illustrates the second configuration example of the nozzle for producing ultrafine fibers which is used in the producing apparatus of FIG. 1. In the first configuration example described above, the second jet outlet 19 is provided concentrically on the periphery of the circular first jet outlet 15. On the other hand, in the second configuration example, the porous metal member 31 is installed in the periphery of the first jet outlet 15, and the holes of the porous metal member 31 act in the same manner as the second jet outlet 19 to generate the second drawing gas stream 17.

It is effective in this configuration to appropriately select the air permeability of the porous metal and maintain the flow speed of the second drawing gas stream 17 in an appropriate range. In this case as well, the desired range of the flow speed ratio of the first drawing gas stream 16 to the second drawing gas stream 17 (second drawing gas stream 17/first drawing gas stream 16) is 1.0 to 0.1.

Since other configurations are the same as those in FIG. 1, the same reference numerals are given to the same components, and a detailed description thereof will be omitted.

Such configured nozzle 10 can also obtain substantially the same operational effects as those of the first configuration example. Additionally, the second configuration example of the nozzle 10 can be similarly applied as the nozzle 10 of the apparatus for producing ultrafine fibers as illustrated in FIG. 1.

Third Configuration Example of the Nozzle

FIG. 5 illustrates the third configuration example of the nozzle for producing ultrafine fibers which is used in the producing apparatus of FIG. 1. In the first configuration example, the flow speed of the second drawing gas stream 17 is controlled based on the pressure difference between the side of the first inlet 14 and second inlet 20 and the side of the first jet outlet 15 and second jet outlet 19, the area ratio of the first inlet 14 to the second inlet 20 of the nozzle 10, and the area ratio of the first jet outlet 15 and the second jet outlet 19 at the tip portion. On the other hand, in the third configuration example, a speed adjustment mechanism 32 that controls the flow speed of the second drawing gas stream 17 is provided in the surroundings of the second inlet 20, and the flow rate of the second drawing gas stream 17 is controlled depending on the generation state of the melted mass of the raw yarn resin. The valve or the regulator, for example, can be used as the speed adjustment mechanism 32.

Since other configurations are the same as those in FIG. 2, the same reference numerals are given to the same components, and a detailed description thereof will be omitted.

Such a configured nozzle 10 can also obtain substantially the same operational effects as those of the first and second configuration examples. Additionally, the third configuration example of the nozzle 10 can be similarly applied as the nozzle 10 of the apparatus for producing ultrafine fibers as illustrated in FIG. 1, and the substantially same operational effects can be obtained.

Second Embodiment

FIG. 6 is a perspective view schematically illustrating the apparatus for producing ultrafine fibers according to the second embodiment of the present invention. In the third configuration example of the nozzle described above, the speed adjustment mechanism 32 is provided to control the flow speed of the second drawing gas stream 17. On the other hand, in the second embodiment, the speed controller 50, the flow rate control device (control device) 51, and the flow rate sensor (air flow sensor) 52 are used for controlling the flow speed of the second drawing gas stream 17.

That is, a hollow-annular-shaped speed adjustment chamber 53 is provided to cover the second inlet 20 of the nozzle 10, and the air is supplied from the speed controller 50 to the speed adjustment chamber 53 through the pipe 54. Under the control of the flow rate control device 51, and based on the air amount or the flow speed detected by the air flow sensor 52, the speed controller 50 supplies the air to the speed adjustment chamber 53 while adjusting the amount of air (an arrow A3) introduced so that the flow speed of the second drawing gas stream 17 becomes a predetermined value. The air introduced into the speed adjustment chamber 53 is supplied to the second inlet 20 of the nozzle 10. Then, the raw fiber fed from the first inlet 14 of the nozzle 10 is guided to the first jet outlet 15, and the second drawing gas stream 17 whose flow speed is controlled is jetted from the second jet outlet 19 to the surroundings of the first drawing gas stream 16. In this state, the laser is irradiated to the raw fiber protruding from the first jet nozzle 15 to partially dissolve the raw fiber, and the melted fiber is drawn by the first drawing gas stream 16 and the second drawing gas stream 17 to produce the ultrafine fibers.

In this way, by performing feedback control on the flow speed of the second drawing gas stream 17, the flow speed of the second drawing gas stream can be controlled more precisely, and the amount of resin mass generated due to poor drawing can be further reduced.

First Modification

In the second embodiment, the flow speed of the second drawing gas stream 17 is controlled by performing feedback control. However, instead of providing the flow rate control device 51 or the flow rate sensor 52, for example, the speed controller with the scale may be provided so that the operator can control the flow rate by manual operation while visually checking the scale.

Third Embodiment

FIG. 7 illustrates the apparatus for producing ultrafine fibers according to the third embodiment of the present invention, and is a schematic configuration diagram of the so-called carbon dioxide gas laser supersonic drawing device for multifilaments. This device simultaneously collects a plurality of nanofibers in the drawing chamber 33 to produce the nanofiber nonwoven fabric 41. The plurality of raw fibers 35 wound around the fiber feed reel 34 are guided from the first inlet to the first jet outlet sides of the respective nozzle portions in the multiple nozzles 100 that function as the fiber feed orifice via the nip roll 36. The multiple nozzles 100 are configured such that n nozzles explained in the first to third configuration examples are arranged in parallel.

The laser irradiation unit 37 on which the multiple nozzles 100 are installed is installed on top of the drawing chamber 33. When the drawing chamber 33 is depressurized by the vacuum pump (not illustrated), the pressure difference between the inside and outside of the drawing chamber 33 causes the air to flow from each nozzle portion into the drawing chamber 33 to generate the first drawing gas stream from the first jet outlet portion. Additionally, the second drawing gas stream which has a slower flow speed than the first drawing gas stream is generated from the second jet outlet portion to the surroundings of the first drawing gas stream.

In this state, the laser is irradiated from the carbon dioxide gas laser oscillator 38 through the irradiation window along the arrangement direction of the nozzle portion to the raw fibers 35 which protrude from the first jet outlet portion of each nozzle portion to partially dissolve the raw fibers 35, and the melted fibers are drawn by the first and second drawing gas streams to simultaneously turn the n fibers into nanofibers. The formed nanofibers are turned into a sheet on the net conveyor 39 to produce the nanofiber nonwoven fabric 41.

Here, as is the case with the first embodiment, the fiber diameter of the nanofibers can be controlled relatively easily by changing the drawing conditions such as the feeding speed of the raw fibers 35, the output of the laser oscillator 38, and the pressure difference between the inlet side and the jet outlet side of the multiple nozzles 100.

Providing the laser irradiation unit 37 protruding from the drawing chamber 33 is not necessarily required, if the laser is irradiated from the window of the drawing chamber 33.

Fourth Configuration Example of the Nozzle

FIG. 8 illustrates the configuration example of the nozzles (multiple nozzles) for producing ultrafine fibers which are used in the producing apparatus of FIG. 7. The multiple nozzles 100 are configured such that n (plural) nozzle portions 10-1, 10-2, . . . , 10-n are arranged in a line. The multiple nozzles 100 have a plurality of first inlet portions 14-1, 14-2, . . . , 14-n arranged on one surface (atmospheric release surface) of the plate-shaped member 110, and a plurality of first jet outlet portions 15-1, 15-2 . . . , 15-n arranged at the positions corresponding to the first inlet portions 14-1, 14-2, . . . , 14-n of the opposing surface (drawing chamber side) of the plate-shaped member 110 and communicate with the respective inlets.

Second passages 18-1, 18-2, . . . , 18-n are formed on the other surface of the plate-shaped member 110. The second jet outlets 19-1, 19-2, . . . , 19-n are provided concentrically on the peripheries of the first jet outlets 15-1, 15-2, . . . , 15-n. In this example, the extended portion 18 a is formed in the second passages 18-1, 18-2, . . . , 18-n to function as the chamber for suppressing the change of flow speed.

Due to the pressure difference between the side of the first inlet portions 14-1, 14-2, . . . , 14-n and the side of the first jet outlet portions 15-1, 15-2, . . . , 15-n, the first drawing gas streams 16-1, 16-2, . . . , 16-n for drawing the melted fibers are generated from the first jet outlet portions 15-1, 15-2, . . . , 15-n respectively, and the second drawing gas streams 17-1, 17-2, . . . , 17-n are generated from the second jet outlet portions 19-1, 19-2, . . . , 19-n.

The individual nozzle portions 10-1, 10-2, . . . , 10-n basically have the same configurations as the nozzle illustrated in FIG. 1. Thus, the same reference numerals are given to the same components, and a detailed description thereof will be omitted.

In such configured multiple nozzles 100, as is the case with the first to third configuration examples, while the second drawing gas streams 17-1, 17-2, . . . , 17-n are generated from the second jet outlet portions 19-1, 19-2, . . . , 19-n to the surroundings of the first drawing gas streams 16-1, 16-2, . . . , 16-n, the laser is irradiated to partially dissolve the raw fibers 35. Consequently, the droplets which cause contaminants and are generated when the fibers are drawn by the first drawing gas streams 16-1, 16-2, . . . , 16-n are blown downward by the second drawing gas streams 17-1, 17-2, . . . , 17-n, and the droplets can be suppressed from adhering to the surroundings of the first jet outlet portions 15-1, 15-2, . . . , 15-n of the nozzle portions 10-1, 10-2, . . . , 10-n. Furthermore, the second drawing gas streams 17-1, 17-2, . . . , 17-n are generated from the second jet outlet portions 19-1, 19-2, . . . , 19-n to the surroundings of the first drawing gas streams 16-1, 16-2, . . . , 16-n so that the vibration ranges of the fibers (vibrators) protruding downward from the first jet outlet portions 15-1, 15-2, . . . , 15-n where the first jet outlet portions 15-1, 15-2, . . . , 15-n serve as the starting point are restricted, and shaking of fibers can be suppressed. Thus, the amount of resin mass generated due to poor drawing can be reduced.

Therefore, the above-described producing apparatus and method require less cleaning of the nozzle portions 10-1, 10-2, . . . , 10-n, and thus, the continuous operation time of the producing apparatus can be extended. Additionally, the resin mass is suppressed from adhering to the product (for example, the nanofiber nonwoven fabric 41) so that the quality can be improved. Moreover, since a large number of nanofibers can be formed from the n nozzle portions 10-1, 10-2, . . . , 10-n respectively, the spinning technology can be further developed, and the nanofiber nonwoven fabric 41 can be efficiently produced.

The conveyor collecting type multi-drawing device which has been described as the example in the fourth configuration example can also be applied to the reel winding type multi-drawing device. The fourth configuration example is also applicable to the continuous winding type multi-drawing device that performs continuous winding by transferring the nanofiber nonwoven fabric collected on the net conveyor to the interlayer paper such as the PET film.

Also, in the fourth configuration example, as is the case with the second and third configuration examples, the porous metal member 31 can be installed in the peripheries of the first jet outlet portions 15-1, 15-2, . . . , 15-n, or the speed adjustment mechanism 32 for controlling the flow speed of the second drawing gas streams 17-1, 17-2, . . . , 17-n may be provided in the surroundings of the second inlet.

Furthermore, as is the case with the second embodiment, the speed controller 50 may be provided to perform feedback control on the flow speed of the second drawing gas stream 17. It is of course possible to provide the speed controller with the scale as in the First Modification to perform flow rate control by manual operation.

(Test Results)

The inventors of the present invention used the conventional nozzle and the nozzle of the present invention to measure and examine the contaminants near the nozzle jet outlet. FIGS. 9A, 9B, and 9C compare and illustrate the adhesion states of contaminants to the nozzles for producing ultrafine fibers of the prior art and of the present invention. Here, the measurement was conducted under the conditions that the pressure difference between the inlet side and the jet outlet side of the nozzle is −70 kPa, the raw fiber thickness is 830 dT, the raw fiber feeding speed is 1.0 m/min, and the vibrator length is approximately 2.5 mm.

FIG. 9A illustrates the conventional nozzle having the 0.8 mm-diameter jet outlet, and the contaminants when the melted fiber was drawn in the drawing gas stream for 15 minutes to produce the ultrafine fibers. The weight of the contaminants adhered at this time was measured, which was 12.6 mg.

FIG. 9B illustrates the double-structure nozzle (corresponding to the first configuration example) in which the second jet outlet with a diameter of 4 mm was formed in the periphery of the first jet outlet with a diameter of 0.8 mm, and the contaminants adhered when the double-structure nozzle drew the melted fiber in first and second drawing gas streams for 15 minutes to produce the ultrafine fibers. The weight of the contaminants adhered at this time was 0.1 mg or less, which could not be measured. The ratio of contaminants to that of the conventional nozzle was reduced 0.008 or less: 1.

FIG. 9C illustrates the double-structure nozzle as illustrated in FIG. 9B and the contaminants adhered when the double-structure nozzle drew the melted fiber in the drawing gas stream for 60 minutes to produce the ultrafine fibers. The weight of the contaminants adhered was 0.1 mg. Therefore, the ratio of contaminants to that the conventional nozzle was reduced to 0.002:1.

It can be seen from this measurement result that the contaminants caused by the adhesion of droplets can be reduced to 1/100 or less to the conventional nozzle.

FIG. 10A is the enlarged image near the jet outlet of FIG. 9A, and FIG. 10B is the enlarged image near the jet outlet of FIG. 9C. In FIG. 10A, 12.5 mg of granular contaminants, that is, the resin mass due to poor drawing is adhered. The ratio of contaminants is 1.0%, and a large amount of resin mass is generated. On the other hand, in FIG. 10B, 0.1 mg of resin mass is adhered, and the ratio of contaminants is 0.1%. The adhesion amount of the resin mass is greatly reduced, and the staple fibers are mainly adhered.

FIG. 11A illustrates the adhesion state of resin mass to the nanofiber nonwoven fabric produced by the conventional producing apparatus, and FIG. 11B illustrates the adhesion state of resin mass to the nanofiber nonwoven fabric produced by the producing apparatus of the present invention. The coverage of the resin mass is 1.2% in the conventional producing apparatus and 0.2% in the present invention. The density is 32 mm⁻² in the conventional art and 9 mm⁻² in the present invention. As compared with the conventional art, the nanofiber sheet produced by the producing apparatus of the present invention has less adhesion of resin mass. In particular, the large-sized resin mass can be greatly reduced.

FIG. 12A illustrates the adhesion state of contaminants to the conventional multiple nozzles (single hole nozzles), and FIG. 12B illustrates the adhesion state of contaminants to the multiple nozzles 100 (corresponding to the fourth configuration example) of the present invention. The amount of contaminants and the ratio of contaminants after 10 minutes of operation are compared and indicated. The amount of contaminants was 0.79 g and the ratio of contaminants was 1.6% in the conventional art, whereas the amount of contaminants was 0.25 g and the ratio of contaminants was 0.5% in the present invention.

However, the amount of contaminants was too small to be measured in the 10-minute operation in the present invention. Thus, the value which was measured after the 30-minute operation was converted to the 10-minute operation.

Although the present invention has been described using the first to third embodiments, the first modification, and the first to fourth nozzle configuration examples, the present invention is not limited thereto. Various modifications are possible without departing from the scope of the invention in the operational phase.

Second Modification

For example, the pressure in the drawing chamber 21 is reduced and feeding of the raw fiber 25 is performed at atmospheric pressure. Instead, the raw fiber feeding chamber may be provided and pressurized to perform drawing at atmospheric pressure. Furthermore, it is clear that the pressure difference can be generated by providing the drawing chamber and the raw fiber feeding chamber. In this case, the relationship expressed by “P2>P1” is satisfied, where P1 is the pressure in the drawing chamber and P2 is the pressure in the feeding chamber of the raw fiber. Additionally, the raw fiber 25 can be fed from the first inlet 14 at atmospheric pressure, and the air can be supplied to the extended portion (chamber) 18 a via the pump or the like. The air pressure P3 in this case is, for example, expressed by “P3>P1” and “P3<P2”.

Third Modification

Additionally, a plurality of slit-like second jet outlets may be provided at the tip portion of the nozzle portion 10 so as to surround the periphery of the first jet outlet 15, and to jet the second drawing gas stream 17 having a slower flow speed than the first drawing gas stream. Various configurations other than the double nozzle structure can be applied, if the second drawing gas stream 17 having a slower flow speed than the first drawing gas stream 16 can be jetted to the periphery of the first drawing gas stream 16 at the time of drawing the melted fiber in the drawing gas stream.

Furthermore, the above embodiments include inventions at various stages, and various inventions may be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some of all constituent elements indicated in the embodiments are deleted, as long as at least one of the problems described in the Problem to be solved by the invention can be solved and at least one of the effects described in the effects of the invention can be obtained, such configuration from which the constituent elements are deleted may be extracted as the invention.

REFERENCE SYMBOL LIST

-   10 Nozzle -   11 Outer nozzle portion -   11 a Internal space -   12 Inner nozzle portion -   13 First passage -   14 First inlet -   15 First jet outlet -   16 First drawing gas stream -   17 Second drawing gas stream -   18 Second passage -   18 a Extended portion (chamber) -   19 Second jet outlet -   20 Second inlet -   21, 33 Drawing chamber -   22 Movable base -   23 Fixed base -   24, 34 Fiber feed reel -   25, 35 Raw fiber -   26, 37 Laser irradiation unit -   27, 38 Carbon dioxide gas laser oscillator -   28 Irradiation window -   29 Transmission window -   30 Power meter -   31 Porous metal member -   32 Speed adjustment mechanism -   36 Nip roll -   39 Net conveyor -   40 Ultrafine fiber (nanofiber) -   41 Nanofiber nonwoven fabric -   50 Speed controller -   51 Flow rate control device (control device) -   52 Flow rate sensor (Air flow sensor) -   53 Speed adjustment chamber -   54 Pipe -   100 Multiple nozzles -   110 Plate-shaped member 

1. An apparatus for producing ultrafine fibers, comprising: a nozzle portion having an inlet for feeding a raw fiber, a first jet outlet which communicates with the inlet and which jets a first drawing gas stream for delivering and drawing the raw fiber, and a second jet outlet which is arranged in a periphery of the first jet outlet and which jets a second drawing gas stream; a laser irradiation unit which is installed on the nozzle portion to irradiate laser light to the raw fiber delivered from the first jet outlet and melt the raw fiber; and a drawing chamber for drawing the melted raw fiber by using the first drawing gas stream and the second drawing gas stream which are jetted from the nozzle portion.
 2. The apparatus for producing ultrafine fibers according to claim 1, wherein the second drawing gas stream has a slower flow speed than the first drawing gas stream.
 3. The apparatus for producing ultrafine fibers according to claim 1, wherein the first and the second drawing gas streams are generated by a pressure difference between inside and outside of the drawing chamber.
 4. The apparatus for producing ultrafine fibers according to claim 1, further comprising a speed adjustment mechanism for controlling a flow speed of the second drawing gas stream.
 5. The apparatus for producing ultrafine fibers according to claim 4, wherein the speed adjustment mechanism includes a valve or a regulator.
 6. The apparatus for producing ultrafine fibers according to claim 1, further comprising a speed controller for adjusting an amount of air flowing to the second jet outlet, wherein the speed controller is operated to control a flow speed of the second drawing gas stream.
 7. The apparatus for producing ultrafine fibers according to claim 1, further comprising a sensor for detecting a flow speed or a flow rate of the second drawing gas stream, a speed controller for adjusting an amount of air flowing to the second jet outlet, and a control device for controlling the speed controller based on the flow speed or the flow rate of the second drawing gas stream detected by the sensor and controlling the flow speed of the second drawing gas stream.
 8. The apparatus for producing ultrafine fibers according to claim 1, wherein the second jet outlet is provided concentrically on the periphery of the circular first jet outlet, and the second drawing gas stream is generated to surround a periphery of the first drawing gas stream.
 9. The apparatus for producing ultrafine fibers according to claim 1, wherein the second jet outlet is holes of a porous metal member installed in the periphery of the first jet outlet.
 10. The apparatus for producing ultrafine fibers according to claim 1, wherein the raw fiber is a monofilament comprising a thermoplastic polymer material, or a multifilament comprising a bundle of a plurality of monofilaments.
 11. The apparatus for producing ultrafine fibers according to claim 1, wherein the nozzle portion includes a plurality of the inlets, the first jet outlets, and the second jet outlets, wherein the second jet outlets are provided in the peripheries of the first jet outlets, respectively.
 12. A method for producing ultrafine fibers, comprising: feeding a raw fiber to an inlet of a nozzle portion and delivering the raw fibers from a first jet outlet which communicates with the inlet to a drawing chamber; irradiating the raw fiber delivered to the drawing chamber with laser light to melt the raw fiber; and drawing the melted raw fiber by using a first drawing gas stream for drawing the raw fiber which is jetted from the first jet outlet and a second drawing gas stream which is jetted from a second jet outlet arranged in a periphery of the first jet outlet.
 13. The method for producing ultrafine fibers according to claim 12, wherein, during the drawing the melted raw fiber, the second drawing gas stream has a slower flow speed than the first drawing gas stream.
 14. The method for producing ultrafine fibers according to claim 12, further comprising feeding the raw fiber to the inlet of the nozzle portion, and generating a pressure difference between inside and outside of the drawing chamber prior to delivering the raw fiber from the first jet outlet which communicates with the inlet to the drawing chamber.
 15. The method for producing ultrafine fibers according to claim 12, wherein the drawing the melted raw fiber includes controlling a flow speed of the second drawing gas stream with a speed adjustment mechanism.
 16. The method for producing ultrafine fibers according to claim 15, wherein the controlling the flow speed of the second drawing gas stream with the speed adjustment mechanism includes controlling the flow speed of the second drawing gas stream with a valve or a regulator.
 17. The method for producing ultrafine fibers according to claim 12, wherein the drawing the melted raw fiber includes operating a speed controller for adjusting an amount of air flowing to the second jet outlet so as to control a flow speed of the second drawing gas stream.
 18. The method for producing ultrafine fibers according to claim 12, wherein the drawing the melted raw fiber further comprises detecting a flow speed or a flow rate of the second drawing gas stream by a sensor; and based on the flow speed or the flow rate of the second drawing gas stream detected by the sensor, controlling a speed controller by a control device to control the flow speed of the second drawing gas stream.
 19. The method for producing ultrafine fibers according to claim 12, wherein the raw fiber is a monofilament comprising a thermoplastic polymer material, or a multifilament comprising a bundle of a plurality of monofilaments.
 20. The method for producing ultrafine fibers according to claim 12, wherein the second jet outlet provided concentrically on the periphery of the circular first jet outlet to draw the melted raw fiber includes generating the second drawing gas stream to surround a periphery of the first drawing gas stream. 